1. Field of the Invention
The invention relates in general to electrical transformers, and more specifically to electrical transformers cooled by a liquid dielectric.
2. Description of the Prior Art
Electrical transformers cooled by a liquid dielectric, such as mineral oil, have cooling ducts formed through the transformer windings in order to direct the liquid as closely as possible to the source of the heat, i.e., the conductor turns. It is conventional to place solid spacers between the turn layers of transformers insulated primarily with cellulosic insulation, with the spacers, which become a permanent part of the winding, supporting the turns and creating gaps or ducts for coolant flow.
In my co-pending application Ser. No. 524,227, filed Aug. 18, 1983, now U.S. Pat. No. 4,503,605, entitled "Cellulose-Free Transformer Coil and Method", which is a continuation of application Ser. No. 264,151, filed May 15, 1981, now abandoned, there is disclosed new and improved cellulose-free winding structures, and methods of constructing such windings, in which the insulation starts out as a liquid resinous insulation and is solidified. The methods disclosed control the formation and size of the voids in the resulting winding structure, such as those due to polymerization shrinkage. My co-pending application discloses constructing an electrical winding in a substantially continuous operation, including the steps of applying liquid resinous insulation to a substrate, quickly solidifying the liquid resin, and immediately applying one or more conductor turns to the just-solidified resin. Cooling ducts are formed by placing solid elongated strips of plastic into the electrical winding as it is being wound. Prior to placing the winding in a transformer tank, the plastic is melted, with the resulting voids forming the cooling ducts.